Brassinosteroids as Central Regulators of Plant Growth, Stress Tolerance, and Agricultural Resilience

Brassinosteroids (BRs) are essential steroidal phytohormones that regulate plant growth, development, and responses to environmental stresses. Recent studies have demonstrated the important roles of BRs in enhancing plant tolerance to abiotic stresses, including drought, salinity, temperature extremes, heavy metal toxicity, and oxidative stress, as well as biotic stresses caused by pathogens and herbivores. This review summarizes current advances in BR biosynthesis, metabolism, transport, and signaling pathways, focusing on key components that mediate stress adaptation. We discuss the physiological and molecular mechanisms through which BRs improve stress tolerance, including regulation of antioxidant defense, ion homeostasis, osmotic adjustment, and stress-responsive gene expression. Particular attention is given to the extensive cross talk between BRs and other phytohormones, such as abscisic acid, jasmonic acid, salicylic acid, ethylene, auxin, and gibberellins, which enables plants to balance growth and defense under adverse conditions. Furthermore, we highlighted the potential applications of BRs in crop improvement through exogenous treatments, genetic engineering, and genome-editing approaches. However, the effectiveness of BR-based strategies is highly dependent on crop species, developmental stage, stress type, BR concentration, application method, and environmental conditions. In addition, excessive BR accumulation or application may result in undesirable growth responses, and further multi-location field validation is required before widespread agricultural implementation. Finally, we discuss emerging research trends, current knowledge gaps, and future perspectives for exploring BR signaling to develop climate-resilient crops. Overall, BRs represent promising targets for improving crop stress resilience; however, optimizing BR-mediated strategies and validating their long-term performance under diverse field conditions will be essential for their successful application in sustainable agriculture.